Two-wheeled, motor-driven transportation, including mopeds and scooters.

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engine backfires at varying speeds, especially when deceleration

1998 royal star motorcycle

When at cruising speeds and when slowing down in deceleration the engine backfires. Have checked all fittings to ensure tight and replaced gaskets. Adjusted carbs to try different fuel air mixtures.

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I have found out that in a multi-carb system, the carburetors need to be synchronized. That eliminated the backfiring.


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ironmonkeyto, Make sure carbs are adjusted correctly and fuel levels are good, one of the biggest reasons for this is if you have an exhaust leak. Check for leaks at all exhaust connections especially at exhaust port/engine connection as well as any cracks/breaks in exhaust system. Good luck.

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timing and valve adjustment can be the issue also

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ironmonkeyto will be eternally grateful.
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